Connecting Fiber-Reinforced Material to an Injection-Moulded Material

ABSTRACT

The invention relates to a process for the bonding of a fiber-reinforced material to an injection-molding material. The invention further relates to an article produced by the process. 
     It is an object of the invention to improve the bond between a fiber-reinforced starting material and a material applied by injection. 
     To achieve the object, further plastics material is inserted under pressure into a fiber-reinforced plastics material. This results in interlock bonding between the further plastics material and the fibers of the fiber-reinforced plastics material. This type of bonding is substantially more stable than the bonding known from the prior art.

The invention relates to a process for the bonding of a fiber-reinforcedplastics material to a further plastics material. The invention furtherrelates to a molding produced by the process.

A process known from the prior art begins, if necessary, by subjecting afiber-reinforced starting material in the form of a sheet to a formingprocess. Plastics material is injected, as can be found by way ofexample in the publication by Sonja Pongratz and Hans Laich “Es mussnicht immer Stahl sein” [It doesn't always have to be steel], inKunststoffe June 2004, in an injection mold onto the starting materialafter it had been subjected to the forming process. Fiber-reinforcedstarting material in the form of a sheet for the purposes of the presentinvention is commercially available, for example from the companyBond-Laminates GmbH in Brilon, Germany. The fibers are composed by wayof example of glass, carbon, or aramid. The material also encompassesthermoplastics or thermosets. Thermoplastics used comprise PA(=polyamide), PBT (=polybutylene terephthalate), TPU (=thermoplasticpolyurethane), PC (=polycarbonate), or PPS (=polyphenylene sulfide), aspublished in November 2005 by way of the Internet on thewww.bond-laminates.com page. This Internet page also reveals that thestarting material can be used for production of moldings via a formingprocess and/or attachments of bonding elements and of reinforcingelements via welding or injection molding.

A disadvantage is that the material applied by injection molding merelyhas adhesive bonding to the starting material that was subjected to theforming process. This type of bonding is relatively unstable.

It is an object of the invention to improve the bonding between afiber-reinforced starting material and a material attached thereto.

The object is achieved via a process with the features of the firstclaim, but also via a molding with the features of the ancillary claims.The invention provides a process for the bonding of a fiber-reinforcedplastics material (2) to a further plastics material, by to some extentinserting the further plastics material (5) under pressure into thefiber-reinforced plastics material.

The invention therefore also provides a molding composed of afiber-reinforced plastics material (2) bonded to a further plasticsmaterial (5) with bonding sites of this type in which fibers (7) of thefiber-reinforced plastics material have been displaced toward theoutside.

Advantageous embodiments are revealed in the subclaims.

To achieve the object, therefore, a further plastics material is to someextent inserted under pressure into a fiber-reinforced plasticsmaterial. The result of this is interlock bonding between the furtherplastics material and the fibers of the fiber-reinforced plasticsmaterial. This type of bonding is substantially more stable than thebonding known from the prior art. That proportion of the furtherplastics material which has not been subject to insertion under pressureforms by way of example a functional element or a reinforcing elementwhich has thus been attached in an improved manner to thefiber-reinforced plastics material.

The plastic of the fiber-reinforced plastics material is preferablysoftened or plasticized. Further plastics material is applied byinjection to the fiber-reinforced plastics material on one side in sucha way that a portion of the further plastics material is pressed outwardat the opposite side. The plastics material applied by injection thusmoves between the fibers of the fiber-reinforced plastics material. Theresult is therefore not only adhesive bonding or weld bonding but alsointerlock bonding between the further plastics material applied byinjection and the fiber-reinforced plastics material.

In one embodiment of the invention, the interlocking bond achievedbetween the further plastics material applied by injection and thefiber-reinforced plastics material merely takes the form of points.Bonding in the form of points can be achieved in a simple technicalmanner, specifically by conventional injection molding.

FIG. 1 shows an injection mold with fiber-reinforced plastics materialintroduced.

FIG. 2 shows a closed injection mold.

FIG. 3 shows a molding produced.

In order to achieve bonding in the form of points by injection molding,a fiber-reinforced plastics material (2) which if necessary has beenpreviously subjected to a suitable forming process is placed in aninjection mold (1). The injection mold (2) has depressions (3). Thelocation of the depressions (3) is behind the fiber-reinforced plasticsmaterial (2) introduced, as is visible in FIG. 1, which shows a sectionthrough the injection mold (1) and the fiber-reinforced plasticsmaterial introduced.

The injection mold (1) is then sealed by a countermold (4). In the caseof thermoplastic, the plastic of the fiber-reinforced plastics materialis softened via a temperature increase. Further plastics material isthen inserted under pressure into the countermold as can be seen in FIG.2, for example using a pressure of from 600 to 1000 bar. Injectedplastics material (5) then penetrates into the fibers of thefiber-reinforced starting material (2) at the sites whose reverse sidehas a depression (3). The result goes beyond the prior art in providinginterlock bonding between the fiber-reinforced plastics material and theinjected plastic.

The fibers of the fiber-reinforced plastics material (2) are regularlydisplaced here in the direction of depression (3), as showndiagrammatically in FIG. 2.

FIG. 3 illustrates some typical features of the resultant molding. Thefiber-reinforced plastics material (2) has a fillet (5) applied byinjection on one of its sides and, on the opposite side, a nub-shapedprotrusion (6), which has been produced by virtue of the depression (3).In this region, the fibers of the fiber-reinforced material (2) havebeen displaced in the direction of the projection (6).

By way of example, this method can be used to apply, by injection, areinforcing rib structure which, at points of inflection or points ofintersection, also has bonding in the form of points via interlockbonding to the fiber-reinforced plastics material.

An injection mold (1) can have depressions (3) in the form of groovesinstead of depressions (3) distributed in the form of points. Interlockbonding is then produced along a groove (3). This method can be used byway of example to achieve complete interlock bonding of ribs to afiber-reinforced plastics material. Projections (6) running in the formof lines are then produced on the opposite side.

If a projection (6) is undesired, it can finally be removed by millingor grinding. The displacement of fibers (7) of the fibrous material in amanner visible in FIG. 3 remains as characteristic feature.

It is preferable to use thermoplastic materials, since these can besoftened by temperature increase. Conventional injection moldingtechniques and injection molding equipment can be adopted for carryingout the process, as long as these can typically withstand pressures of1000 bar.

Thermoplastic materials with particularly good suitability for theconduct of the invention are PA 6,6, PA 6, PBT, PP (=polypropylene), PET(=polyethylene terephthalate), PA 12, PPS, TPU or PA 4,6. Preference istherefore given to semicrystalline plastics with low viscosity which arenot susceptible to internal stresses. However, some amorphous materialsare also suitable, and specifically and especially PS (=polystyrene),ABS (=acrylonitrile-butadiene-styrene), and/or PC. The plasticsmentioned can also be mixed with one another.

A desired forming process for fiber-reinforced plastics materialpreferably takes place in an injection mold (1) via sealing with acounter-mold (4), giving a particularly low-cost production process. Itis preferable that the fiber-reinforced plastics material is preheated,prior to its insertion, to a temperature which exceeds the melting pointof the plastic by from 20 to 40° C. Melting point here means at leastthe temperature required to permit injection of the plastic in theinjection molding process. The result is firstly that thefiber-reinforced plastics material can readily undergo a formingprocess. Secondly, the plastic is not liquefied to the extent thathandling becomes difficult. Lower temperatures during the formingprocess are possible, but this makes the forming step more difficult.

In order to achieve particularly stable interlock bonding, thefiber-reinforced material has continuous-filament fibers which havepreferably been braided with one another. The fiber-reinforced plasticsmaterial then has, for example, fibers in the form of a textile.

Fiber-reinforced plastics materials with particularly good suitabilitytake the form of sheet-like starting material whose wall thickness isfrom 0.5 to 6 mm. If the starting material is too thick, it is thendifficult to impress the plastics material into the fibers. Excessivelythin starting material does not have sufficient stability.

The inventive process permits the production of components from a singlematerial. An article produced according to the invention is thentherefore composed of only one plastic. This simplifies recycling.

One embodiment of the process uses application by injection in order tobond two fiber-reinforced plastics materials in the form of sheets toone another. This gives two partially superposed sheets. Plastic isapplied by injection from one side in such a way that plastic from oneof the sheets penetrates into the fibers of the other sheet. This givesparticularly stable bonding.

In order to make a further improvement in the total stability ofarticles produced in one embodiment of the invention, plastics materialmixed with fibers is bonded to the fiber-reinforced plastics material.The further plastics material then uses chopped fibers whose averageinitial fiber length is preferably from 2 to 15 mm. The average initialfiber length is particularly preferably from 2 to 3 mm, in order toobtain particularly good results. The lengths of the fibers used becomeshorter by virtue of the further processing, and specifically andregularly by a factor of 10. The average fiber length in the productproduced is therefore regularly from a few tens of μm to 2 mm. It ispreferably not only the average length that is within the stated rangebut also all or most of the individual fibers.

The invention is preferably used to produce oil pans, for example formotor vehicles, with external rib structure. The ribs have inter aliainterlock bonding to the container. The ribs serve for absorption ofenergy in the event of stone impact, and also in the event of anaccident, in order to prevent damage to the container. They thereforeprovide particularly dependable protection of the container and are notmerely broken away when the oil pan is subject to stone impact duringtravel. According to the invention, it is then equally possible toattach a fastening collar for the oil pan. There are no corrosionproblems, and this is another factor favoring production of an oil panfrom plastic.

The bonds produced according to the invention are, and remain,dependably impermeable to liquid and gas. Another preferred applicationsector is provided by articles in which importance is placed on bondswhich are dependably impermeable to liquid and/or gas. An example of onepreferred application sector is therefore bulkheads which protect theinterior of a car from water penetration.

The mold costs for carrying out the process are relatively low. However,production is relatively slow. According to the invention it istherefore preferable to produce articles which are produced withrelatively small numbers of units. The overall production of these canbe achieved at lower cost when comparison is made with alternativeproduction processes. One preferred application sector is thereforecomponents of trucks and niche-market cars such as cabriolets, in orderto replace components hitherto entirely or to some extent produced frommetal. For the purposes of the invention, the numbers of units producedof these vehicles are small.

The bond is not damaged by temperature variations. Another preferredapplication sector is therefore moldings or articles which have exposureto temperature variations, which the bonds have to resist. The inventioncan therefore by way of example also be used in moldings for aircraft.

Another typical field of application for the invention is protectivehelmets with fastening elements or rib structures. Fastening elementsare attached according to the invention. By way of example, thefastening elements serve to fasten a visor on the helmet or Styropor®within the helmet.

Inventive examples started from commercially available, fiber-reinforcedthermoplastic materials in the form of sheet from Bond-Laminate GmbH.The thickness of the sheets was 2 mm. The sheets were rectangular, withlength 380 mm and width 128 mm. They had three holes which served forpositioning in the injection mold. The plastics material used comprisedinter alia PA6. The fibers were composed of glass, carbon, or aramid.

The sheets were preheated for 3 minutes at 300° C. in an oven andinserted into an injection mold. The mold temperature set was 95°Celsius. The shape of the injection mold was such as to permitproduction of the substrate reinforced with ribs 8. Behind the insertedfiber-reinforced starting material there were, in the injection mold—ascan be seen from FIGS. 1 and 2—circular recesses 3 at a distance of 5.5cm with diameter 9 mm and depth 1 mm. Closure of the injection moldfirst brought about a forming process on the fiber-reinforced startingmaterial and this was followed by injection of furtherglass-fiber-reinforced PA 6 plastics material using an injection rate of120 mm/s. The injection pressure was initially 900 bar for one second.The post-injection pressure was 600 bar for a further 8 seconds. After acooling time of 30 seconds, the injection mold was opened and thesubstrate produced, reinforced with ribs, was ejected. The ribs 8 hadalso been bonded in the form of points to the fiber-reinforced materialvia interlock bonding in the manner visible in FIG. 3. FIG. 3 shows asection of a substrate thus produced. The fillet 5 represents a point ofintersection of two intersecting ribs 8. FIG. 4 shows a section of asubstrate produced, seen from the lower side. Ribs 8 also have interlockbonding in the form of points by way of the fillets 5 to thefiber-reinforced starting material 2. The result was therefore asubstantially stronger bond between the fiber-reinforced startingmaterial 2 and the other plastics material, when comparison is made withthe prior art mentioned in the introduction.

1. A process for bonding a fiber-reinforced plastics material to afurther plastics material, comprising to some extent inserting thefurther plastics material under pressure into the fiber-reinforcedplastics material.
 2. The process as claimed in claim 1, in which thefurther plastic is inserted under pressure in the form of points orlines into the fiber-reinforced plastics material.
 3. The process asclaimed in claim 1, in which the fiber-reinforced plastics material issoftened or plasticized prior to the inserting.
 4. The process asclaimed in claim 1, in which the fiber-reinforced plastics material isthermoplastic, and the fiber-reinforced plastics material is heated,prior to the inserting, to a temperature which is at most 20° C. abovethe melting point of the thermoplastic.
 5. The process as claimed inclaim 1, in which the bonding is achieved via injection molding.
 6. Theprocess as claimed in claim 5, which further comprises introducing thefiber-reinforced plastics material into an injection mold which, behindthe fiber-reinforced plastics material introduced, has one or moredepressions, and inserting the further plastics material under pressureinto the fiber-reinforced plastics material from an opposite side. 7.The process as claimed in claim 6, which further comprises, by virtue ofa pressure of the further plastics material, moving plastic materialinto the depressions.
 8. The process as claimed in claim 1, whichfurther comprises preheating fiber-reinforced, thermoplastic material toa temperature which is from 20 to 40° C. above the melting point of thethermoplastic material, and subjecting the preheated thermoplasticmaterial to a forming process in an injection mold.
 9. The process asclaimed in claim 1, in which the plastic used comprises PA 6,6, PA 6,PBT, PP, PET, PA 12, PPS, TPU and/or PA 4,6, or a mixture thereof. 10.The process as claimed in claim 1, in which the plastic used comprisesPS, ABS, and/or PC, or a mixture thereof.
 11. A molding composed of afiber-reinforced plastics material bonded to a further plastics materialwith bonding sites in which fibers of the fiber-reinforced plasticsmaterial have been displaced toward an outside of the molding.
 12. Themolding as claimed in claim 11, in which the fibers have been displacedin the direction of an adjacent protrusion protruding toward theoutside.
 13. The molding as claimed in claim 11, in which the plastic isthermoplastic.
 14. The molding as claimed in claim 11, in which thefiber-reinforced plastics material is thermoplastic material havingcontinuous-filament fibers.
 15. The molding as claimed in claim 11,wherein the fiber-reinforced material has a thickness from 0.5 to 6 mm.16. The molding as claimed in claim 11, wherein the fiber-reinforcedplastic is reinforced by chopped fibers whose average fiber length isfrom 10 to 300 μm.
 17. The molding as claimed in claim 11, which is anoil pan, a bulkhead or a helmet.